Web.config files are not identical on all machines in the farm (SharePoint Server)
APPLIES TO: 
2013 2016 2019 Subscription Edition 
SharePoint in Microsoft 365
Rule Name: Web.config files are not identical on all machines in the farm.
Summary: If you have multiple front-end Web servers in the farm and have made manual changes to the Web.config files, you will experience a problem where a front-end Web server cannot read session state that was saved by another server in the farm.
Cause: The Web.config files on the front-end Web servers in the farm are not identical.
Resolution: Ensure that the Web.config files are identical on all front-end Web servers in the farm.
Verify that the user account that is performing this procedure is a member of the Farm Administrators group.
Identify the server on which this event occurs. On the SharePoint Central Administration website, in the Monitoring section, click Review problems and solutions, and then find the name of the server in the Failing Servers column. If there are multiple failing servers in a server farm, you must repeat the following steps on each failing server.
Verify that the user account that is performing the following steps is a member of the Administrators group on the local computer that you identified in the previous step.
Log on to the server on which this event occurs.
Typically the Web.config file is stored at
C:\inetpub\wwwroot\wss\VirtualDirectories\Port_Number. Note the modified date of the Web.config file.Repeat the previous steps on other failing servers.
Compare these Web.config files and decide which one is correct. To view the content of the Web.config file, do the following:
In Server Manager, click Tools, and then click Internet Information Services (IIS) Manager.
In the Internet Information Services management console, in the Connections pane, expand the tree view of the server name, expand Sites, and then click the site for which you want to view the settings of the Web.config file.
On the site Home page, switch to the Features View, and then in the Management section, double-click Configuration Editor.
In the Section list, select a section to view the settings of the Web.config file.
Delete the incorrect Web.config file on each failing server, and then copy and paste the correct Web.config file.
By default, the Repair Automatically option is enabled for this rule. You can restore the default setting for this rule by doing the following:
Restore default setting
In Central Administration, click Monitoring.
On the Monitoring page, in the Health Analyzer section, click Review rule definitions.
On the Health Analyzer Rule Definitions - All Rules page, in the Category: Configuration section, click the name of the rule.
In the Health Analyzer Rule Definitions dialog, click Edit Item.
Select the Repair Automatically check box, and then click Save.